Wing and a scare: The mysterious UFO that shocked plane passengers as it was filmed zooming around them

If it’s an April Fool's joke, it’s a few days too late.
A mysterious round white object was filmed whizzing around a passenger plane above Seoul, the capital of South Korea, on April 7.
The clip, which has been uploaded to YouTube, begins with the ‘craft’ at the bottom of the screen, keeping pace with the passenger plane.
But then it speeds up and rises in altitude before zipping off out of shot, just as the startled person filming it tries to zoom in for a closer look.